The present invention relates generally to the field of optical communications. More specifically, the present invention relates to a fine pointing assembly for a steering mirror, which is used in an optical inter-satellite communications system.
Weight, volumetric displacement and power are critical parameters when designing for satellite-based communications equipment. Higher weight, volumetric displacement and power consumption may lead to higher spacecraft and launch costs and/or reduced payload capacity. Satellite-based communications equipment must also be reliable and durable due to the obvious problem that it will be inaccessible for servicing.
Optical inter-satellite communications systems require steering mechanisms that must provide a large articulation range on two axes (azimuth and elevation) and, at the same time, extreme accuracy and stability. For example, accuracy to within 1 micro-radian may be required. Also, in systems that require rapid scanning or tracking in an unstable (noisy) environment, the steering mechanism must be capable of operating with a high closed-loop bandwidth.
It is an object of the preferred embodiment of the present invention to provide a fine pointing assembly for directing a light beam in an optical inter-satellite communications system.
It is a further object of the preferred embodiment of the present invention to provide a fine pointing assembly that has a small volumetric displacement.
It is a further object of the preferred embodiment of the present invention to provide a fine pointing assembly that is low weight.
It is another object of the preferred embodiment of the present invention to provide a fine pointing assembly that is power efficient.
It is another object of the preferred embodiment of the present invention to provide a fine pointing assembly that is reliable and durable.
It is still another object of the preferred embodiment of the present invention to provide a fine pointing assembly that is accurate, stable and capable of directing a light beam over a large articulation range in two axes.
It is still another object of the preferred embodiment of the present invention to provide a fine pointing assembly that is capable of high closed-loop bandwidth operation.
These and other objects of the present invention are provided by a fine pointing assembly for steering a light beam in an optical inter-satellite communications system. The fine pointing assembly includes a mirror connected to an assembly housing by an outer gimbal, an inner gimbal and a set of linear motors. The inner gimbal is pivotally connected to the housing and the outer gimbal is pivotally connected to the inner gimbal. A position sensor and signal conditioning circuitry located within the housing sense the position of the mirror a provide feedback position signals used in the control of the linear motors.
In one embodiment of the present invention the inner gimbal may be connected to the housing by one or more flexure pivots. The outer gimbal may also be connected to the inner gimbal by one or more flexure pivots.
To ensure reliability and durability, the position sensor may comprise a primary position sensor and a redundant position sensor. The signal conditioning circuitry may also comprise primary signal conditioning circuitry and redundant signal conditioning circuitry. The linear motors may comprise primary motor windings and redundant motor windings.
The position sensor may be of any known type of position sensor but preferably comprises a capacitive sensor for improved accuracy.
According to a preferred embodiment of the present invention, the entire fine pointing assembly for pointing a representative 1.5 inch diameter mirror displaces less than approximately 8 cubic inches.
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.